Rails 3：与多态关联的多对多关系

Question

我有 2 个模型，例如任务模型和任务关系模型 Task 有很多父任务和子任务。

已添加以下关联 -

Task.rb

  has_many :from_tasks, :as => :relation, :class_name => "TaskRelation", 
                        :foreign_key => "task_from_id", :source => :parent, 
                        :conditions => {:relation_type => 'Parent'}, :dependent => :destroy
  has_many :to_tasks , :as => :relation, :class_name => "TaskRelation", 
                       :foreign_key => "task_to_id", :source => :child, 
                       :conditions => {:relation_type => 'Child'}, :dependent => :destroy
  has_many :child_tasks, :through => :from_tasks, :dependent => :destroy
  has_many :parent_tasks, :through => :to_tasks, :dependent => :destroy

  accepts_nested_attributes_for :to_tasks, :reject_if => :all_blank, :allow_destroy => true
  accepts_nested_attributes_for :from_tasks, :reject_if => :all_blank, :allow_destroy => true

TaskRelation.rb

  belongs_to :parent_task, :class_name => "Task",  :foreign_key => "task_from_id"
  belongs_to :child_task, :class_name => "Task", :foreign_key => "task_to_id"
  belongs_to :relation, :polymorphic => true

当我保存任务表单时，它还会将 parent_tasks 和子任务保存在 task_relations 表中，其中关系类型为“任务”，但我想将关系类型存储为父任务的“父”和子任务的“子”。

谁能帮帮我。

Answer 1

首先，删除 relation 多态关联 - 它不是必需的。现在，将您的 Task 模型修改为如下所示：

# This association relates to tasks that are parents of self
has_many :parent_task_relations, class_name: 'TaskRelation', foreign_key: 'child_task_id'
# And this association relates to tasks that are children of self
has_many :child_task_relations, class_name: 'TaskRelation', foreign_key: 'parent_task_id'

has_many :child_tasks, :through => :child_task_relations
has_many :parent_tasks, :through => :parent_task_relations

你应该完成了。

为了说明如何使用它 - 假设您有一个任务 a 并且需要将任务 B 分配为父任务，并将任务 C 分配为子任务。你可以这样做：

a.parent_tasks << b
a.child_tasks << c

这将对您的数据库产生与此代码相同的效果：

a.parent_task_relations.create(parent_task: b)
a.child_task_relations.create(child_task: c)

这与（对数据库）相同：

TaskRelation.create(parent_task: b, child_task: a)
TaskRelation.create(parent_task: a, child_task: c)